I can’t imagine a by-law that banned owners from writing to each other would survive much scrutiny at a Tribunal, and your strata committee can’t just issue fines or costs claims with a Notice To Comply.
Does the NTC mention a specific by-law (it should) and what does that by-law say?
Either of our strata law sponsors – Sachs Gerace or Bannermans would handle this with ease. Give them a call and ask how much it would cost.